Long-Term Debt and Finance Leases - Summary (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018	Jul. 17, 2017	May 31, 2017
Long-Term Debt and Capital Leases
Available borrowing capacity	$ 229.5
Long-term debt	2,295.6	$ 2,300.9
Finance lease liability	12.1
Capital lease obligations		5.1
Total long-term debt and finance lease obligations	2,307.7	2,306.0
Debt issuance costs, net	(9.3)	(10.5)
Sub-total	2,298.4	2,295.5
Less current portion	(26.9)	(24.1)
Long-term portion	$ 2,271.5	2,271.4
Term B Loans
Long-Term Debt and Capital Leases
Effective interest rate (as a percent)	5.84%
Long-term debt	$ 2,230.6	2,240.9
Debt issuance costs, net	(6.9)
Net discount	9.5
Revolving Credit Facility
Long-Term Debt and Capital Leases
Available borrowing capacity	$ 229.5
Effective interest rate (as a percent)	5.40%
Long-term debt	$ 65.0	$ 60.0
Debt issuance costs, net	(2.4)
Maximum borrowing capacity	300.0		$ 300.0	$ 200.0
Outstanding letters of credit	$ 5.5